Adding A Ventilation System to your Home Can Improve Asthma

If you are an adult living with asthma, your home might sound like a safe zone where flare-ups can be controlled–but is that true?  The truth is, many chemicals used or created in your home can contribute to flare-ups, especially by well-intended but uninformed family members, roommates or neighbors.   These include:

• Personal products like body sprays, perfumes, fragranced soaps and lotions

• Cleaning products

• Cooking without ventilation

• Plug-in fragrances, candles and incense

• Sweeping or vacuuming without a HEPA vacuum

These produce fine particulates and VOCs that are harmful to asthmatic lungs.

Source: Effects of residential ventilation and filtration interventions on adult asthma outcomes

A recent study explored the effects of 3 different ventilation systems to see if/how they improved asthma outcomes.  If you didn’t know, ventilation “dilutes” indoor air pollution by adding fresh air to the total quantity of indoor air, making pollutants less concentrated.  Although dilution is not the solution to indoor air pollution (see an interesting visual demonstration here), it is helpful when the indoor sources of pollution are difficult to control (bad roommates, neighbors, or family members).

The study compassed 40 homes, with 51 participants total.  The majority of these homes were “bungalows” in Chicago, built prior to the 1950s, with masonry frames and 1 to 1.5 stories. (Chicago’s “bungalow belt” consists of almost 80,000 homes constructed in the 1920s that are similar in style, size, and construction.) The study homes were distributed across 23 Chicago community areas, and each home received one of three interventions: Group 1 received continuous energy recovery ventilators (ERVs: 12 homes); Group 2 received intermittent central-fan-integrated supply (CFIS: 15 homes) systems, and Group 3 received continuous bathroom exhaust fan(s) (13 homes).  In addition, homes with ERV or CFIS systems also received central air filtration upgrades to MERV 10 filters, which were replaced quarterly.  In all homes, indoor and outdoor air pollutants were measured quarterly, and Asthma Control Test (ACT) scores were collected monthly and health-related quality of life and stress were assessed at the beginning and end of the study.  Here are diagrams of how they work:

To explain these systems, ERVs take outside air and run it through a heat exchanger and air filter, to make it more similar to the indoor temperature and quality.  Some of the indoor air is also exhausted to the outdoors, so that the total volume of air in the home stays the same (hence a neutral pressure).  The CFIS systems were set to run once per hour for 15-20 minutes, also taking outdoor air and filtering it, but not removing any indoor air.  The bath fans (Group 3) did not receive filtration upgrades because of a lack of central forced-air heating or cooling systems. 

As you can see, there are 3 different types of pressure acting on the homes because of the ventilation strategy: neutral (ERV), positive pressure or exfiltration (with CFIS) and negative pressure or infiltration (with bath fan).  In our experience today, neutral or positive pressure is always preferable, because outside air (and the crevices it comes through in negative air pressure situations) can be dirty.  (The homes in the study, being built before the 1950s, were almost guaranteed to be “leaky” homes).  We’ve advised against negative pressure ventilation in more than one article.  In suburban and urban settings, like the study area, ultrafine particulates and nitrogen oxides (NOx) from traffic and industry can be drawn into the home and aggravate asthma.   Groups 1 and 2 had this outside ventilation air filtered, whereas Group 3 did not.

Correspondingly, the asthmatics with ERVs had the greatest improvements, with an 8.4 % increase in ACT scores and an increase in the proportion of participants with well-controlled asthma from 50 % to 86 %.  The CFIS group showed 7.1% improvement in their ACT scores, and the bath fan group showed 3.8% improvement in their ACT scores.  

Even though Group 3 had the most modest improvement, it seems that a continuously-operating bath fan with no filter, seems to be better than no ventilation at all.  It has been shown in multiple studies that NO2 (nitrogen dioxide) from gas stoves is particularly aggravating for asthma.  Ninety percent of the homes studied used a gas stove.  Therefore, continuously extracting indoor air that contains NO2 from cooking with a gas stove and replacing it with outdoor air is better than not using any ventilation.

What are the lessons here for those who are trying to control asthma?  First, if you like to cook with a gas stove, check out our article here and make sure you have and USE an exhaust fan during and after cooking.  Second, having a central air conditioning or heating system in your home makes it easier to introduce ventilation (ERV or CFIS) that has the most meaningful impact on your asthma control.  Third, even if you don’t have a central air conditioning or heating system, just using your exhaust fans regularly can make a small difference in your asthma control, because getting harmful gases and particulates out of your breathing zone is important.